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Deck Stairs Calculator

Building stairs for your deck is often considered “the most difficult part of” the construction project. Having the right calculations before getting started can make the task a lot easier.

To simplify the process, we’ve created this deck stair calculator to help you determine the correct measurements needed to carry out your project. Before we look at the specific measurements we’ll need, it helps to understand more about the various parts of deck stairs.

What Are the Parts of a Deck Staircase?

Knowing the lingo behind the parts that make up a staircase can go a long way toward taking accurate measurements and simplifying the process.

The key components of a set of deck steps are:

Treads are horizontal boards that create the footing area for each step

Risers are boards that cover the vertical distance between stair treads

Stringers are the boards that run diagonally on either side of a staircase. Treads and risers are fixed to these stringers to create a stable structure for a set of stairs.

A landing pad is an optional part of your deck’s staircase. If your staircase is directly above a flat surface made of concrete or gravel, you may not need to construct a landing pad.

Use the calculator to add your deck’s measurements for:

Total rise (height from the top of your deck to the ground, which accounts for the vertical distance between the treads of each step)

Step run (horizontal tread depth) for each stair

Tread type (whether you’ll use a single board or two smaller boards to create a stair tread)

Stringer attachment style (whether you plan to use an outside frame or a flush frame)

Pro Tip: A shorter rise may be more comfortable to climb with a deeper run. Similarly, a taller rise might work better with a shorter run. Check your local building codes for allowable rise and run.

How to Calculate Stair Stringers

Having a stable, sturdy set of stairs leading to and from your deck is one of the most important -- and complex -- parts of the deck building process. To calculate the stringer length, follow this formula:

(run)2 + (stair rise)2 = [square root of your total]

Total Rise (Deck height to ground)

Feet

Inches

Inches

Step Run (Tread Depth)

Inches

Inches

Tread Type

2 - 5/4x6

2 - 2x6

1 - 2x12

Deck Joist Size

2x6

2x8

2x10

2x12

Stringer Attachment

Outside Frame

Outside Frame - Flush

Build your DIY carpentry knowledge and check our article on building deck stairs and steps. You’ll find tips and tricks to help make your deck building project run more smoothly.